This work aims to compare the chemical composition and anti-inflammatory effects on RAW264.7 macrophages of Keemun black tea stems and leaves. Fifty volatile compounds were identified in tea stems and leaves, and aldehydes, alcohols, and esters were the main volatile compound categories. Eleven key volatile compounds, including geraniol, phenylacetaldehyde, methyl salicylate, linalool, etc. contributed to distinguishing the tea stems from the tea leaves. In the quantitative and LC-MS-based metabolomics analysis, higher contents of amino acids, monosaccharides, and quinic acid were found in stems than in leaves. Inversely, higher contents of tea pigments, flavan-3-ols, gallic acid, purine alkaloids, and flavonol glycosides were present in tea leaves than in stems. LC-MS-based metabolomics also revealed that organic acids were the most critical non-volatile compounds responsible for the differences between tea stems and leaves. Furthermore, tea stems had better inhibiting effects of pro-inflammatory cytokines (IL-1β and IL-6) in lipopolysaccharide-challenged RAW264.7 macrophages than tea leaves, while no significant differences exist between leaves and stems for inhibiting the secretion of TNF-α and NO. In conclusion, our results support using Keemun black tea stems as a novel source of anti-inflammatory compounds.

Larger-leaf yellow tea (LYT) is a characteristic type of Chinese tea produced in Huoshan County, Anhui Province, which is made by mature leaves with stems. According to recent report, LYT showed competitive effects in anti-hyperglycemia in comparison to other teas such as green or black tea. However, the bioactive compounds of LYT are still undiscovered so far. For this purpose, 5 fractions of LYT were prepared by sequential extraction. The in vitro bioassay results indicated that the ethyl acetate fraction of LYT had the strongest inhibitory effects on α-glucosidase and α-amylase. Fluorescence-quenching analysis and protein-binding test revealed that the compounds of ethyl acetate fraction could inhibit α-glucosidase and α-amylase activities through binding to enzymes or other mechanisms. All chromatographic peaks of high-performance liquid chromatography (HPLC) of ethyl acetate fraction were separated and collected. The purified compounds were identified by liquid chromatography-mass spectrometry (LC-MS), and subsequently screened by calculating their inhibition ratio on α-glucosidase at the real concentration in LYT infusion. The results showed that (–)-epigallocatechin gallate, (–)-gallocatechin gallate, caffeine, N-ethyl-2-pyrrolidone-substituted flavan-3-ols were effective inhibitors for α-glucosidase.

Roasting is a common manufacture technology for processing various teas. It is not only used in decreasing the water content of finished tea, but also improving the flavor of teas. In the present study, the roasted and non-roasted teas were compared by liquid-chromatography mass spectrometry and sensory evaluation. The roasted tea tasted less bitter and astringent. The content of main galloylated and simple catechins, caffeine and theobromine in roasted were significantly lower than non-roasted teas. Targeted taste-compounds metabolomics revealed that (–)-epigallocatechin gallate, kaempferol-glucose-rhamnose-glucose and (–)-epicatechin gallate were main contributors tightly correlated to astringent intensity. Flavonol glycosides including kaempferol-glucose, quercetin-glucose, kaempferol-glucose-rhamnose-glucose, and quercetin-glucose-rhamnose-glucose in roasted teas were also significantly less than non-roasted teas. To study the chemical changes during roasting, tea with a strong astringency was roasted under 80, 100, 120, 140, and 160 ℃. With the increase of roasting temperature, the bitter and astringent intensity of tea was gradually decreased, but the main astringent compounds including (–)-epigallocatechin, (–)-epigallocatechin gallate and kaempferol/quercetin glycosides were irregularly varied with temperature. The Pearson correlation coefficient analysis suggested procyanidin B2, coumaroylquinic acids and gallotannins were tightly correlated to the astringent and bitter perceptions, while N-ethyl-2-pyrrolidone-substituted flavan-3-ols were negatively correlated.